The long range goal of this project is to characterize the mechanism(s) by which gene expression is regulated in eukaryotic organisms using the Saccharomyces yeast as model eukaryotes and the fermenatation of maltose as a model regulated system. The fermentation of maltose in Saccharomyces utilizes two enzyme functions: maltose permease an maltase. The expression of the structural genes encoding these enzyme is induced by maltose and repressed by glucose. In order to ferment maltose a strain must carry any one of five unlinked MAL loci. We have extensivley characterized the MAL6 locus and shown it to encode three genes: MAL61. encoding maltose permease; MAL62. encoding maltase; and MAL63, encoding a positive regulatory function controlling the expression of both structural genes. In this proposal we plan to: (1) Complete the transcriptional analysis of the MAL6 locus. (2) Define the upstream sequences controlling the expression of the structural genes, MAL61, and MAL62. (3) Characterize the functinal domains of the MAL63 gene product, particularly its DNA binding activity. (4) Analyze the MAL64-constitutive mutations and determine the mechanism of mutation ativating this MAL64 gene product in the constitutive mutations. (5) Identify new genes encoding products which interact with the MAL61 -MAL62 controlling sequences or with the MAL63 gene product and thus also involved in the regulation of gene expression of these structural genes.